A well known and widely-used clinical reagent for the detection of occult blood in a sample, particularly a faecal sample, is guaiac (also known as gum guaiac or resin guaiac). When used in association with an appropriate developer solution, guaiac provides a colorimetric assay system for detecting haemoglobin in the sample. Such tests are commercially available, for example, Hemoccult II and Hemoccult II Sensa (SmithKline Diagnostics, San Jose, Calif., USA).
Prior Australian Patent No. 665956 (International Patent Application No. PCT/US92/04425) notes that among the many analytical systems used for detection and/or determination of analytes, particularly analytes of biological interest, are chromatographic assay systems. Among the analytes of biological interest frequently assayed with such systems are:    1. hormones, such as human chorionic gonadotropin (hCG), frequently assayed as a marker of human pregnancy;    2. antigens, particularly antigens specific to bacterial, viral, and protozoan pathogens, such as Streptococcus, hepatitis virus, and Giardia;     3. antibodies, particularly antibodies induced as a result of infection with pathogens, such as antibody to the bacterium Helicobacter pylori and to human immunodeficiency virus (HIV);    4. other proteins, such as haemoglobin, frequently assayed in determinations of faecal occult blood, an early indicator of gastrointestinal disorders such as colon cancer;    5. enzymes, such as aspartate aminotransferase, lactate dehydrogenase, alkaline phosphatase, and glutamate dehydrogenase, frequently assayed as indicators of physiological function and tissue damage;    6. drugs, both therapeutic drugs, such as antibiotics, tranquillisers and anticonvulsants, and illegal drugs of abuse, such as cocaine, heroin, and marijuana; and    7. vitamins.
Such chromatographic systems are frequently used by physicians and medical technicians for rapid in-office diagnosis and therapeutic monitoring of a variety of conditions and disorders. They are also increasingly used by patients themselves for at-home monitoring of such conditions and disorders.
Among the most important of such chromatographic systems are the “thin layer” membrane-based systems in which a solvent moves as a solvent front across a thin, flat absorbent medium (e.g., nitrocellulose membrane). Among the most important of tests that can be performed with such thin layer systems are immunoassays, which depend on the specific interaction between an antigen or hapten and a corresponding antibody. The use of immunoassays as a means of testing for the presence and/or amount of clinically important molecules has been known for some time.
Chromatographic techniques used in conjunction with immunoassays include a procedure known as immunochromatography. In general, this technique uses a disclosing reagent or particle that has been linked to an antibody to the analyte to be assayed, forming a conjugate. This conjugate is then mixed with a specimen and, if the analyte to be assayed is present in the specimen, the disclosing reagent-linked antibodies bind to the analyte to be assayed, thereby giving an indication that the analyte to be assayed is present. The disclosing reagent or particle can be identifiable by colour, magnetic properties, radioactivity, specific reactivity with another molecule, or another physical or chemical property. The specific reactions that are employed vary with the nature of the analyte being assayed and the sample to be tested.
The present invention is particularly, but not exclusively, directed to collection of samples derived from faecal material for occult blood detection, for example in screening for colorectal cancer. As previously described, guaiac testing provides a colorimetric assay system for detection of haemoglobin in a sample, however because of the large number of false positives obtained in guaiac testing, in screening programs the use of two or three guaiac tests has been recommended, confirmed when positive by an immunological test for human haemoglobin (Favennic L., Kapel N., Meillet D., Chochillon C. and Gobert J. G., Annales de Biologie Clinique, 50(5):311-3, 1992). More recently, a combination of guaiac and immunological testing has been suggested (Allison, J. E., Tekawa, I. S., Ransom, L. J. and Adrian, L. L. N. Engl. J. Med., 334:155-9, 1996).
It is an object of the present invention to provide a sample collection method which is simple and economic, and which enables subsequent detection and/or determination of analyte in the sample to be readily carried out, for example using a guaiac test, and/or an immunochromatographic or other immunodiagnostic procedure.